Conventionally, image display apparatuses such as projectors have been widely used. For example, light from light sources is modulated by a light modulator such as a liquid-crystal device and the modulated light is projected on a screen or the like, such that an image is displayed. A reflective liquid-crystal display device, a transmissive liquid-crystal crystal device, a DMD (Digital Micromirror Device), or the like is used as the light modulator.
As projectors for presentation or digital cinema, more and more products have recently employed solid-state light sources such as LEDs (Light Emitting Diodes) and LDs (Laser Diodes), not the conventional mercury-vapor lamps, xenon lamps, and the like, as the light sources. It is relatively easy for the solid-state light sources such as the LEDs and LDs to increase the luminance. They are long-lasting, which leads to less frequent lamp replacement. They have an advantage in that they light up immediately after powered on.
Patent Document 1 has disclosed a technology by which it is possible to address a safety problem in that, regarding a projector including laser light sources, user's or image observer's eyes are exposed to projected light with a high luminance (e.g., paragraph, FIG. 2, etc. of Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-open No. 2013-54370